Bypassing the cooling fan

[JerryMaidstone]

Hi all. I have a 1984 1900cc water cooled T25. When stuck in traffic the fan comes on but not before the engine has got very hot. My cure, would be to fit an additional switch in the cab, so that I could override the system and turn on the fan sooner. Does anyone have wiring ideas please, Jerry

[Smiffo]

It would depend on whether you have a 3pin ( 2 speed fan ) or 2 pin ( Single speed fan ) setup, but the principle would be the same.

Basically - unless someone tells me I am wrong - I would imagine you would fit a switch in parallel to the wires going to rad switch.
Fitting that way should leave the fan to activate automatically when needed, but also allow you to manually select the fan to come on if you want.

When you say `hot` though, how hot?
Maybe it is normal and you are over cautious, or maybe the rad temp sensor is on its way out?

I am sure someone will be able advise a test of the sensor, although I suspect it is just easier to replace it for the low cost of replacements and agro factor of testing the old one...
( If you replace it, and do it quickly, you won't lose much coolant - taking the old one to test could be a ball ache. )

[Mocki]

Yeah common mod, known as a "chicken switch"

The switch in the rad , as I'm sure you know is not connected in anyway to the temp gauge , or the engine other than by the coolant .
It's normal for the rad fan not to cut in before 3/4 of the gauge , so many fit the bypass switch .
Personally I've never felt the need , generally speaking if your cooling system is in good order and your rad is working well ( not crudded up ) mr VW did a good job and it works well .

[CovKid]

Chicken switch. Can't see it? Check out where the dash dimmer normally is. My rad fan kicks in ok but must admit my finger has hovered over that switch a couple of times. Nice thing to have in dire emergency and the dimmer no longer had a use in mine.

[Smiffo]

Why is it called a Chicken Switch..!??

Because you chicken out and flick the switch before the rad switch does it for you..??

[CovKid]

Got it in one. Suits those amongst us that have had a boil-over and not got over it.

[Smiffo]

Got it in one. Suits those amongst us that have had a boil-over and not got over it.

I might fit one to my sump, then I can chicken out and dump oil on the road - James Bond style - before my engine does..!!

[JerryMaidstone]

Thanks all for your help

[CovKid]

If you do have a 2 speed fan, best to wire the chicken switch to the high speed one. That way if you do have a panic in the cockpit, you can be sure the temperature will come down fast. I've used mine a couple of times in bumper-to-bumper traffic in Summer but I'm planning to dump the rad switch and install a more intelligent sensor with accurate adjustment for fan kick-in point rather than the fixed nature of the rad switch but just have too many projects on the go at mo to tackle it. Maybe later in the year. Rad fan switches don't tend to have a long life span.

Some will (rightly) argue that the stock version does the job but it was 30 years ago and theres room for improvement in my view. Chicken switches are a simple belt n braces approach and it does no harm to have one, although everything should work correctly if all is in good order.

Well worth getting a temperature gun - really helps in terms of seeing if things are kicking in when they should. Plus good for reading temperature of kids (at a distance) when they try to convince you they're too ill to go to school.

[tobydog]

Organic overide